1. Field of the Invention
The invention relates to a device for improving the spatial resolution of a micropore optics system for x-rays.
2. Discussion of Background Information
In the construction of a telescope for x-rays the problem arises that no suitable lenses exist for x-ray radiation because of the low refraction and the strong absorption in matter. Mirrors in the conventional sense cannot be used either, since the reflectivity for x-rays, unlike for visible light, is too low by far. Adequate reflectivity values result only for very large angles of incidence close to 90 degrees. This effect can be used to build a reflecting telescope for x-rays, provided that suitably designed surfaces are found. The x-rays must thereby strike the reflecting surface at a very small angle (e.g., grazing incidence), since x-rays are reflected by polished surfaces only when the incidence of the rays is almost grazing. One possibility for realizing an x-ray telescope is therefore to use a parabolic reflector. However, the parabolic reflector has very large image errors under the conditions of a grazing incidence.
A Wolter Type I telescope is known from the prior art (see, e.g., the publication “Spiegelsysteme streifenden Einfalls als abbildende Optiken für Röntgenstrahlen,” H. Wolter, Analen der Physik, 10, 1952, p. 94-114). A telescope of this type utilizes the reflection of x-ray radiation with grazing incidence on metal surfaces. The basic concept is that a hyperboloid is placed behind the paraboloid as a correcting reflector, on which hyperboloid the x-rays are reflected for a second time.
The mirror arrangement of the Wolter Type I (e.g., Wolter-I) is composed of metallic (e.g., often comprising only coated foils) paraboloids of revolution multiply nested within one another, each of which is followed by a hyperboloid of revolution. These mirrors together have similar imaging properties like conventional telescopes in the visible range of light. The rays are first reflected on a small section of a parabolic reflector and subsequently on a section of a hyperbolic reflector. In order to achieve greater intensities, several mirror systems of this type were nested within one another, since, due to the grazing incidence, each pair of mirrors has only a very narrow range in which it can collect x-ray light and focus it in the focal point. For example, in the mirror system of the ROSAT x-ray satellite, four Wolter double mirrors with the same focal length are nested within one another in order to obtain a large collecting area.
An approximation of the Wolter-I optics is known from the prior art. The approximation uses several stacks of cylindrical areas with single tilt, which replaces the paraboloids and hyperboloids. This type of approximation can be tolerated if large focal lengths are chosen.
Furthermore, an x-ray lens has hitherto been produced by a pore optics system, the reflecting surfaces of which an ideal Wolter-I optics system approximates through two cylindrical areas. A pore optics system of this type is shown in FIGS. 1A and 1B. An approximation occurs for production-relevant reasons. In the pore optics system, the cylindrical mirror shells 12 are applied layer by layer on a cylindrical base 10, as shown in FIG. 1A (see FIG. 1B). A mirror shell is polished on the front face and provided on the back with many webs 14. The webs 14 of the mirror shell 12 last applied are connected to the mirror surface of the mirror shell 12 lying underneath, so that the last mirror surface is curved exactly like the one underneath it. This production method requires the spaces remaining between the webs 14 and the mirror shells 12, the pores, to have a rectangular cross section.
The advantage of a pore optics system is to be able to produce many mirror shells precisely and to mount them one behind the other. The mirror shells are connected to one another by webs, which leads to the geometry of many small pores. However, one disadvantage of the prior art is that the spatial resolution of the x-ray optics of known solutions no longer meets current requirements.